Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, which are particularly suitable for use in a broadcasting television camera, a cinema camera, a video camera, and a digital still camera.
Description of the Related Art
In recent years, as an image pickup apparatus such as a television camera, a cinema camera, a video camera, or a film camera, a large format camera having features of a shallow depth of field and beautiful bokeh (blur) quality for expanding visual expression is used. As a zoom lens to be attached to the large format camera, a small and lightweight zoom lens having a large aperture, a high zoom ratio, and high optical performance for securing mobility and improving flexibility in photography and visual expression has been in demand. Especially in photographing, producing, and the like of a nature program, in order to photograph a facial expression of an animal, a bird, or the like from a distance, a telephoto zoom lens capable of covering angle of fields in a super telephoto range has been in demand. As the telephoto zoom lens having the high zoom ratio to be attached to the large format camera, as proposed in Japanese Patent Application Laid-Open No. 2007-139858, Japanese Patent Application Laid-Open No. 2004-085846, and Japanese Patent Application Laid-Open No. 2011-175185, a positive-lead type zoom lens including four or more lens units in total, of which a lens unit having a positive refractive power is arranged closest to an object side, has been known.
In Japanese Patent Application Laid-Open No. 2007-139858, a zoom lens including four lens units and having an angle of field at a telephoto end of about 0.7 degree and a zoom ratio of about 15× has been proposed.
In Japanese Patent Application Laid-Open No. 2004-085846, a zoom lens including four lens units and having an angle of field at a telephoto end of about 1.6 degrees and a zoom ratio of about 3× has been proposed.
In Japanese Patent Application Laid-Open No. 2011-175185, a zoom lens having a magnification ratio of about 5×, and a half angle of field at a telephoto end of about 3 degrees has been disclosed.
In general, when an image size of the image pickup apparatus becomes larger, the zoom lens to be attached thereto is accordingly increased in size. Therefore, as a zoom lens to be attached to a large format camera, in order to attain improvements in mobility and flexibility in photography and attain a large aperture ratio and the high zoom ratio at the same time, reductions in size and weight of the zoom lens become objects to be achieved. In order to reduce the size and weight of the zoom lens, it is important to downsize a first lens unit having a largest lens diameter, and a zooming lens unit, which increases in movement amount as the zoom ratio is increased.
In regard to the zoom lens disclosed in Japanese Patent Application Laid-Open No. 2007-139858, as a problem in adapting to an even larger image pickup element and increasing the zoom ratio while maintaining the large aperture ratio, an effective diameter of the zooming lens unit is increased and a mechanism for driving the zooming lens unit is increased in size, which makes it difficult to downsize the zoom lens.
In regard to the zoom lens disclosed in Japanese Patent Application Laid-Open No. 2004-085846, as a problem in further increasing the zoom ratio, it is difficult to suppress a movement amount of a third lens unit for correcting an image plane, and in addition, a total lens thickness of a first lens unit is large, which makes it difficult to downsize the zoom lens.
In regard to the zoom lens disclosed in Japanese Patent Application Laid-Open No. 2011-175185, in order to realize a further increase in magnification, a movement amount of a second lens unit accompanying zooming is increased, which makes it difficult to realize both the increase in magnification and the reductions in size and weight.
In order to realize both the increase in magnification and the reductions in size and weight, it is important to appropriately set refractive powers of the first lens unit and the second lens unit in particular.